CNS antigen presentation.

Presentation of antigens for the CNS follows the same general rules as for other tissues. However, the presence of special CNS cells with immune functions plus the blood-brain barrier (BBB) suggests that differences in the way that the immune system functions in the CNS might help to explain why some autoimmune diseases are unique to the CNS. Irrespective of whether CNS antigen presentation takes place inside or outside the CNS (or both), the BBB clearly plays a major role in CNS immune function. The BBB governs the quantity and type of lymphocytes that enter the CNS by way of specific adhesion-molecule binding between lymphocytes and endothelium and possibly by selecting for antigen-specific lymphocytes in antigen-recognition events.